A digital-to-analog converter (DAC) is an electronic circuit that converts an input digital signal to an output analog signal. A numerical value represented by the digital signal input to the DAC corresponds with a magnitude of the analog signal output by the DAC. Various factors determine the performance of a DAC, including speed, resolution, and noise. Resolution refers to the smallest incremental signal that is generated by the DAC and corresponds with the Least Significant Bit (LSB) of the input digital signal. Noise refers to deviations of the output analog signal relative to an expected or desired level, particularly during switching from one digital value to another.
High performance DACs are useful for converting data with high resolution at high frequency and low noise. High performance DACs are used to generate a variety of signal outputs, including ascending and descending ramps and sinewaves. Typically, separate DACs are implemented to generate the various signal outputs. Various methods have been used in an attempt to improve behavior and performance, but many such conventional techniques introduce increased costs or increased size allocation.
Many prior art current-steering DACs are implemented using a segmented architecture. This architecture of the DAC is divided into two sub-DACs: the LSBs are implemented using a binary architecture while the most significant bits (MSBs) are implemented in a unary way. The major differential nonlinearity (DNL) errors occur during the transition of all LSBs to each MSB. DNL is the deviation between two analog values corresponding to adjacent input digital values. In many systems, the MSB current source needs to be matched to the sum of all the current sources of LSBs to within a small error range, for example 0.5 LSB. Because of statistical spread, such matching is difficult to achieve.
A frequency-modulated continuous-wave (“FMCW”) radar system often uses a highly linear frequency ramp to provide accurate range and velocity information. The resolution of the ranging information is directly dependent on the linearity of the transmit signal as the transmit signal is also used to detect the signal received from the target. The output of the voltage-controlled oscillator (“VCO”) that is used to generate the radar signal is typically non-linear. Therefore, digital-to-analog controller architecture for controlling the chirp linearity of the radar system is desired.
The figures are not intended to be exhaustive or to limit the invention to the precise form disclosed. It should be understood that the invention can be practiced with modification and alteration, and that the invention be limited only by the claims and the equivalents thereof.